And to speak strictly, a Man that holds his breath is weightier while his lungs are full, then upon expiration. For a bladder blown is weightier then one empty, and if it contain a quart, expressed and emptied it will abate about a quarter of a grain. And therefore we somewhat mistrust the experiment of a pumice stone taken up by _Montanus_, in his Comment upon _Avicenna_, where declaring how the rarity of parts, and numerosity of pores, occasioneth a lightness in bodies, he affirms that a pumice-stone powdered, is lighter then one entire; which is an experiment beyond our satisfaction; for beside that abatement can hardly be avoided in the Trituration; if a bladder of good capacity will scarce include a grain of air, a pumice of three or four dragms, cannot be presumed to contain the hundred part thereof; which will not be sensible upon the exactest beams we use. Nor is it to be taken strictly which is delivered by the learned Lord _Verulam_, and referred unto further experiment; That a dissolution of Iron in _aqua fortis_, will bear as good weight as their bodies did before, notwithstanding a great deal of waste by a thick vapour that issueth during the working; for we cannot find it to hold neither in Iron nor Copper, which is dissolved with less ebullition; and hereof we made trial in Scales of good exactness: wherein if there be a defect, or such as will not turn upon quarter grains, there may be frequent mistakes in experiments of this nature. That also may be considered which is delivered by _Hamerus Poppius_[SN: Basilica Antimonii.], that _Antimony_ calcin'd or reduced to ashes by a burning glass, although it emit a gross and ponderous exhalation, doth rather exceed then abate its former gravity. Nevertheless, strange it is; how very little and almost insensible abatement there will be sometimes in such operations, or rather some encrease, as in the refining of metals, in the test of bone ashes, according to experience: and in a burnt brick, as _Monsieur de Clave_[SN: Des Pierres.] affirmeth. Mistake may be made in this way of trial, when the _Antimony_ is not weighed immediately upon the calcination; but permitted the air, it imbibeth the humidity thereof, and so repaireth its gravity. CHAPTER VIII Of the passage of Meat and Drink.